Back in the early '90s, my best friend Liz had one of those Hypercolor T-shirts. If you remember them, you'll know they turned from bright pink to bright green depending on the body heat of the wearer. (I think Liz only wore the shirt to school once due to the unfortunate effect of it working too well. You could see a perfect outline of her bra under her shirt because it was cooler than the rest of her skin.)

But a new company, The UnSeen, is using similar color-changing technologies for a raft of interesting projects that go way beyond trendy tricks. They've inserted color-changing molecules into fabrics to show pollution, atmospheric conditions (for an astronaut patch), wind, touch and more.

The company's latest innovation, unveiled at London Fashion Week, is a temporary hair color that reacts to ambient temperatures. It comes in several changing shades, including Fire, which turns from black (cold) to red (hot); black to white; silver to blue; blue to white; and black to yellow. You can see how it works in the video below, but it reacts to both ambient temperature (moving from cooler outside air to a warm room) and also the user's temperature — meaning if you blush, your hair color will change too.

Lauren Bowker is the chemist-mastermind behind the company; in fact, she's known in fashion circles as "The Alchemist." Bowker looked at how the human skin regulates temperature and then created a carbon-based molecule that can undergo a reversible reaction when the temperature rises or falls. Bowker says she was inspired by a scene in the '90s film "The Craft" in which one of the main characters casts a spell that allows easy hair color changes.

But this isn't magic; it's chemistry.

How it works

“Above a certain temperature, one of the molecule forms is more stable than the other, and so a reaction takes place producing a molecule with a slightly different absorption of light, and thus a different color… Essentially, the active part of the dye system is a complex carbon based molecule, which undergoes a reversible reaction with itself,” Bowker told Forbes.

Previous thermochromic inks have been highly toxic to human skin, so Bowker had to reformulate. Her product is made from "less toxic ingredients" though the specific details of those ingredients have not been revealed. The product is undergoing testing and formulation so it can be made commercially available. (Good news for all of us who want to try it!)

"Because of how we've formulated the dye, we're confident there will be no damage to the scalp, and no significant effect on the hair fibres themselves (no more then typical semi permanent dyes that is.)" Bowker told Wired.

Beyond creating a fun new way to play with hair, Bowker hopes to inspire more young women into the creative world of STEM careers.

“I really believe it's a great example of a product that celebrates women in science and to encourage young females to see the opportunity for creativity within science and engineering — bringing sci-fi to real life!” Bowker told Forbes.

You can learn more about how the company came into being and how it uses chemistry to create "reactive" fashion like the pollution jacket in this fascinating video below:

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.